1. Field of the Invention
The present invention relates to an ultrasonic oscillator having a layered structure of internal electrodes with piezoelectric elements and in particular to an ultrasonic oscillator enabling a miniaturization by a comprisal of specific electrode wiring.
2. Description of the Related Art
In recent years, ultrasonic motors have been in the spot light as new motors replacing electromagnetic motors. An ultrasonic motor has an advantage over a conventional electromagnetic motor in terms of (a) gaining a high thrust at low speeds without a reduction gear; (b) large holding force; (c) a long stroke and high resolution; (d) a low noise emission; (e) no magnetic noise emission or susceptible to noise, et cetera.
The inventing entity of the present invention has proposed one basic comprisal of conventional ultrasonic motor with such advantages, namely, a linear ultrasonic motor using an ultrasonic oscillator (e.g., refer to a Japanese patent laid-open application publication No. 07-163162; refer to paragraphs 0035 through 0040, FIGS. 7 and 18).
Also proposed, while taking advantage of the above noted characteristics, is an ultrasonic motor used for a drive power source for a camera cone of a camera by integrating an oscillator with the camera cone, which is the lens holding member, so as to advance or retract the camera cone against a fixed shaft by the oscillator (e.g., refer to a Japanese patent laid-open application publication No. 08-179184; refer to the abstract, and FIG. 1).
Let it describe the basic comprisal of the conventional ultrasonic oscillator and ultrasonic motor at this moment.
FIG. 1 describes an example comprisal of ultrasonic oscillator for use in the conventional ultrasonic motor, with the top part being an exploded perspective view of basic substantial part of the ultrasonic oscillator and the bottom part being a front view of assembled ultrasonic oscillator.
The ultrasonic oscillator 1 shown by the bottom part of FIG. 1 is made up of plural layers of thin rectangular piezoelectric plates 2, with a first piezoelectric plate 2a being printed by a pair of electrodes, i.e., upper internal electrode 3a and lower internal electrode 3b, and with a second piezoelectric plate 2b being printed by a pair of electrodes, i.e., upper internal electrode 3c and lower internal electrode 3d, and having a structure of layering the first piezoelectric plates 2a and second piezoelectric plate 2b alternately.
And the ultrasonic oscillator 1 is installed by a piezoelectric plate 4 at the front part of the layer of the first piezoelectric plate 2a and the second piezoelectric plate 2b, at the center part thereof and the back part thereof, respectively, with these piezoelectric plates 4 with no electrode and the one layered at the center part featuring a hole 5 at an approximate position of the common nodes between a longitudinal oscillation and bending oscillation.
The above described upper internal electrode 3a and lower internal electrode 3b are formed to extend to the front side of the ultrasonic oscillator 1 (as shown by FIG. 1), while the upper internal electrode 3c and lower internal electrode 3d are formed to extend to the rear side thereof.
Each of these piezoelectric plates 2a and 2b is made by printing an electrode on a green sheet of PZT, followed by positioning, layering and baking. Subsequently, four of external electrodes 6 are placed, as positive electrodes, on the side surface where the upper internal electrode 3a and lower internal electrode 3b of the ultrasonic oscillator 1 expose themselves onto, while four thereof are placed, as negative electrodes, on the far side surface where the upper internal electrode 3c and lower internal electrode 3d expose themselves onto as shown by the bottom part of FIG. 1.
And, the external electrode 6 placed on the top left of the front side is connected with the one placed on the bottom right by way of a lead wire 7 in order to form a phase-A (positive pole), while the external electrode 6 placed on the top right of the front side is likewise connected with the one placed on the bottom left by way of another lead wire 7 in order to form a phase-B (positive pole).
While not shown herein, other four external electrodes 6 placed on the rear side of the ultrasonic oscillator 1 are also connected likewise in order to form a phase-A (negative pole) and phase-B (negative pole). An application of DC voltage to the electrodes phases-A and -B carries out a polarization processing.
And, a drive contact unit 8 is adhered onto the lower surface of the ultrasonic oscillator 1 at a point where the amplitude of later described bending oscillation comes to an approximate maximum, and another drive contact unit 8 is adhered onto the upper surface thereof at a point where the amplitude of bending oscillation comes to an approximate maximum.
An ultrasonic oscillator 1 with the drive contact units 8 being adhered as shown by the bottom part of FIG. 1 will be called as such, while one without a drive contact unit 8 (i.e., a comprisal shown by the top part of FIG. 1 is stacked together and baked, followed by completing the connection with the external electrodes by lead wires) will be called an oscillator body 1a, hereinafter respectively.
In the above described comprisal of the ultrasonic oscillator 1, an application of alternate voltage to the phases-A and -B of external electrodes 6 with the phase difference of π/2 will excite a large elliptic oscillation at the above described points of the drive contact units 8.
The top and center parts of FIG. 2 are diagonal perspective views illustratively describing an ultrasonic elliptic oscillation of the oscillator body 1a of the ultrasonic oscillator 1 oscillated by applying a voltage to the electrodes comprised as above described, and the bottom part thereof shows the bi-dimensional bending oscillation shown by the center part thereof only by contour lines of the oscillator body for easier understanding.
First, an application of alternate voltage, of the same phase, in the neighborhood of resonance frequency to the phase-A electrodes 6 and 6, and phase-B electrodes 6 and 6, of the ultrasonic oscillator 1 shown by the lower part of FIG. 1, excites a unidimensional longitudinal oscillation made up of a stationary position 8 and resonance bending oscillation position 9. In this event, the oscillator body 1a mainly expands & contracts in the longitudinal direction and at the same time the sizes of the up to down, and the left to right, of the center part expands & contracts.
Also in the lower part of FIG. 1, an application of alternate voltage, of opposite phase, in the neighborhood of resonance frequency to the above described phase-A electrodes 6 and 6, and phase-B electrodes 6 and 6 excites a bidimensional bending oscillation made up of a stationary position 11 and resonance bending oscillation position 12 in the oscillator body 1a as shown by the center part of FIG. 2. In this event, the parts of the oscillator body 1a are oscillating mainly in the up and down directions as shown by the drawing.
These oscillations have been estimated by a computer analysis using a finite element method, with a result of ultrasonic oscillation testing actually having backed it up.
Incidentally, the bottom part of FIG. 2 also shows the movements of two drive contact units 13 mounted onto the upper and lower surfaces, respectively, of the oscillator body 1a shown by the bottom part of FIG. 1, in addition to the stationary position 11 and resonance bending oscillation position 12.
In order to transmit power from the oscillator body 1a to a drive support member in high efficiency, the drive contact units 13 shall be desirably placed fixedly at a position, or nearby, where the oscillation of the ultrasonic oscillator 1 in the direction opposite to the drive support member becomes the highest as shown.
The top and center parts of FIG. 2 also show a pin member 15 mounted into the hole 5 (shown by the bottom part of FIG. 1) which has been featured at the position of the center part 14 which comes to a node of oscillation shown by the bottom part of FIG. 2.
FIG. 3 shows illustratively an elliptic oscillation of the drive contact unit 13 of the ultrasonic oscillator 1 when applying an alternate voltage in the neighborhood of the resonance frequency with the phase difference of π/2.
Note that FIG. 3 shows a connected type which connects drive contact units 13 with a plate member 16. Also note that the below described movement of elliptic oscillation is the same if the drive contact units 13 were respectively independent drive contact units unconnected by a plate member 16.
The top part of FIG. 3 shows an action in the case of the phase of alternate voltage applied to the phase-A electrodes 6 and 6 is in advance of that to the phase-B electrodes 6 and 6 by π/2, with the drive contact units 13 mounted onto the bottom surface of the oscillator body 1a rotating CCW (counterclockwise), while the drive contact units 13 mounted onto the top surface thereof rotating CW (clockwise).
And the bottom part of FIG. 3 shows an action in the case of the phase of alternate voltage applied to the phase-A electrodes 6 and 6 is behind that to the phase-B electrodes 6 and 6 by π/2, with the drive contact units 13 mounted onto the bottom surface of the oscillator body 1a rotating CW, while the drive contact units 13 mounted onto the top surface thereof rotating CCW.
As described above, it is desirable to place the drive contact units 13 on the same surface of the oscillator body 1a so as to rotate in the same direction and at the same time place the drive contact units 13 on the opposite side so as to rotate in the opposite direction. This makes it possible to take out a relative drive force vis-à-vis the drive support member most effectively.
FIG. 4 shows a basic form of engagement between an ultrasonic oscillator and two shafts which are drive support members in an ultrasonic linear motor. Note that the showing of FIG. 4 assigns the same component numbers where the configuration is the same as that of FIG. 3, and omits some components shown by FIG. 1 such as the external electrodes.
In FIG. 4, the ultrasonic oscillator 1 is sandwiched between a stationary shaft 17-1 on the top and movable shaft 17-2 on the bottom, with a coil spring 18 applying force upwards on the both ends of the movable shaft 17-2.
And the form of contacting engagement between the drive contact units 13 and shafts 17 (i.e., 17-1 and 17-2) on the top and bottom, respectively, is such that the contacting part between the guide shaft 17 in the form of a round shaft and convex of the drive contact units 13 is circular in compliance with the outer shape of the round guide shaft 17.
By this, an elliptic oscillation compounded by the longitudinal oscillation and bending oscillation of the oscillator body 1a acts on the shafts 17 which sandwich the ultrasonic oscillator 1 by way of four of the drive contact units 13 from the top and bottom so as to advance or retract the ultrasonic oscillator 1 in the left or right directions in the way delineated by the drawing along the guide between the round outer shape of the shafts 17 and circular concave contact surface of each drive contact unit 13 of the ultrasonic oscillator 1.
While not shown in FIG. 4, the ultrasonic oscillator 1 is installed by a pin member 15 protrusively off the side surface thereof as shown by the top and center parts of FIG. 2. Supporting the upper and lower shafts 17 (i.e., 17-1 and 17-2) and the coil spring 18 by a main apparatus, and connecting the pin member 15 with a driven member will make the driven member advance or retract in the same direction as advancing or retracting movement of the ultrasonic oscillator 1 vis-à-vis the upper and lower shafts 17.
Or, supporting the pin member 15 by the main apparatus and connecting the driven member with the upper and lower shafts 17 (i.e., 17-l and 17-2) and the support member of the coil springs 18 will make the driven member advance or retract in the same direction as advancing or retracting movement of the upper and lower shafts 17, i.e., leftward and rightward, driven by the ultrasonic oscillator 1. This is the principle of operation of an ultrasonic linear motor. In the above described ultrasonic linear motor, the ultrasonic oscillator has a vital role after all. For instance, in the case of using an ultrasonic motor as a drive source for advancing and retracting movement of the lens frame of a digital camera with a rapid change to downsizing, a miniaturization of ultrasonic oscillator as the heart of ultrasonic motor is an urgent need.